(1) Field of the Invention
This invention relates to a filming liquid composition, in particular to a filming liquid composition usable to manufacture color Braun tubes which exhibit significantly increased luminescent brightness of fluorescent screen.
(2) Description of the Prior Art
In general, a method of manufacture for a fluorescent film of a color Braun tube comprises forming on the inner face of the Braun tube a fluorescent screen with a uniform stripe or dot pattern of green phosphor, blue phosphor and red phosphor, thereafter forming an aluminium vacuum evaporation film on the fluorescent screen.
However, the surface of the formed fluorescent screen is not even because of the gaps between the phosphor stripes or dots, which leads to a problem in that the vacuum evaporated aluminium will penetrate into the phosphors so as to lower the mirror reflection effect of the aluminium film if aluminium film is formed directly on the fluorescent screen.
In order to solve this problem, the gaps between the phosphor stripes or dots are covered with a special coating liquid, which is a so-called filming.
The filming technology is described by way of example in Japanese Patent Publication No. Sho. 57-31614 and 61-696.
In the prior art, a filming liquid composition generally comprises an acrylic emulsion as a major ingredient and polyvinyl alcohol as a cross-linking agent. However, those filming liquid compositions of the prior art have caused a problem that the organic materials such as polyvinyl alcohol were decomposed to generate a gas in the calcining process subsequent to the aluminium vacuum evaporation, and the gas caused a swelling of the aluminium film to lower the evenness of the aluminium film, thereby decreasing the mirror reflection effect. Thus, the brightness of the color Braun tube was relatively low.
In addition to this, the filming liquid of the prior art with a high pH value must be used to increase the adhesive power of the filming film, but these filming liquid compositions with a high pH value have suffered the gellation of polyvinyl alcohol in the composition.